Fast Least-Squares Reverse Time Migration of OBN Down-Going Multiples

Yanbao Zhang,Jia Yi,Yike Liu,Xuejian Liu

doi:10.3389/feart.2021.730476

Abstract

Nowadays the ocean bottom node (OBN) acquisition is widely used in oil and gas resource exploration and seismic monitoring. Conventional imaging algorithms of OBN data mainly focus on the processing of up-going primaries and down-going first-order multiples. Up-going multiples and higher-order down-going multiples are generally regarded as noise and should be eliminated or ignored in conventional migration methods. However, multiples carry abundant information about subsurface structures where primaries cannot achieve. To take full advantage of multiples, we propose a migration method using OBN down-going all-order multiples. And then the least-squares optimization algorithm is used to suppress crosstalks. Finally, a phase-encoding-based migration algorithm is developed to cut down the computational cost by blending several common receiver gathers together using random time delays and polarity reversals. Numerical experiments on the complex Marmousi model illustrate that the developed approach can enlarge the imaging area evidently, reduce the computational cost effectively, and enhance the image quality by suppressing crosstalks and improving the resolution.

Highlights

Many advanced imaging algorithms have been developed over the past few decades, among which reverse time migration (RTM) can provide quality images of subsurface complex structures aided by the two-way wave equation
To make full use of the structural information contained in multiples and further increase the illumination range, we proposed RTM using down-going multiples for ocean bottom node (OBN) acquisition, in which the lowerorder multiples are recognized as the secondary sources of the higher-order multiples
The second one is the RTM of controlledorder multiples (RTM-CM) in which the different orders of multiples are extracted before migration procedures and the separated nth-order and (n+1)th-order multiples respectively act as the source and receiver data

Summary

INTRODUCTION

Many advanced imaging algorithms have been developed over the past few decades, among which reverse time migration (RTM) can provide quality images of subsurface complex structures aided by the two-way wave equation. We use five sets of supergathers that regard the number of encoding CRGs as the variable to present the effectivity and efficiency of the proposed phase-encoding-based LSRTM of down-going multiples. Compared with the RTM, the LSRTM can effectively suppress the noise caused by the interferences among encoded CRGs (the noise term of Eq 12) and significantly improve the imaging resolution as shown by the arrows in panels A and B of Figures 12–16. The comparison of computational cost demonstrates that the proposed phased-encoded LSRTM method can provide the results which can meet the requirement of interpretation and improve the computational efficiency manyfold

DISCUSSION

DATA AVAILABILITY STATEMENT

CONCLUSION